1. Field of the Invention
The present invention generally relates to apparatus and methods for the irradiation of both food and non-food products, and more specifically to an apparatus and method for irradiating food which includes an integrated transport and irradiation system for irradiating large quantities of produce and other food products.
2. Discussion of Prior Art
The irradiation of food has developed as an industry over a period of approximately 30 years. At the present time, FDA regulations have been promulgated for irradiating wheat, wheat flour, potatoes, pork, and produce. These regulations provide for giving absorbed radiation doses to food (other than spices) of up to 100 kilorads. It is expected that eventually many additional foods will be cleared for irradiation for preservation and other beneficial purposes, in addition to disinfestation purposes. A wide spectrum of food products will be covered under such regulations, including, e.g., meats and poultry. It is expected that any approval given by FDA to irradiate for such purposes will permit foods to be exposed to higher levels of radiation than are now used for disinfestation in order to achieve the desired beneficial purposes.
It is common in the design of irradiators to utilize radioisotopic sources, e.g., Cobalt-60 and Cesium-137. Recently, Cesium-137 sources have been made available through the Department of Energy; and these sources are generally in the form of WESF capsules containing 40-50 kilocuries.
Standard irradiators are generally designed to accommodate existing standardized packaging for given food products. As a result, these designs generally provide for a pallet containing a plurality of cartons of packaged food products which are adapted to be disassembled, with the cartons thereafter being individually fed through the irradiator; and, upon completion of an irradiation process, the cartons are re-palletized. During the course of irradiation, the cartons of products will be conducted over multiple passes in which they are exposed to gamma-irradiation in various dose distributions, such that the cumulative effect of the radiation is to irradiate all of the product within the container to a minimum dose level which will be sufficient to kill or sterilize appropriate insects in various stages of life. The irradiator design is required to provide less than a maximum dose level to the product so as to be safely within FDA regulatory imposed limits; as well as to minimize any deleterious effects to the food, such as phytotoxicity which will adversely effect citrus fruits.
In handling such cartons of material, additional costs are required for labor, machinery and equipment necessary to de-palletize the cartons, to handle the cartons individually, and to place the cartons on and remove them from a conveyor system, as well as to re-palletize the cartons on pallets after taking them from the conveyor.
Conventional irradiator devices have been adequate in meeting minimum and maximum dose requirements to food products while efficiently utilizing radiation from the radioisotopic sources. To obtain higher efficiency irradiators, it is necessary that the cartons be positioned on a conveyor in a substantially continuous fashion so that the length of travel of the cartons through the irradiator, and any unnecessary delays, will be minimized. Conventional irradiator designs are thus fairly complex in their conveyor and transport mechanisms. Additionally, conventional irradiator apparatus include an undesirably large number of moving parts, e.g., pneumatic cylinders, and there are consequently problems of radiation damage to the components and to lubricants for the components, which create increased maintenance problems.
Recently, the Environmental Protection Agency has banned the use of ethylene dibromide for use on citrus fruits, and it therefore appears that the most viable substitute to the disinfestation of citrus fruits will be irradiation processing. The throughput requirements for irradiators having a size capable of handling significant percentages of citrus fruit crops will have to be quite large, and it is likely that throughputs on the order of 100,000 pounds per hour may be required.
Conventional irradiation systems, which depend upon conveyors and complicated travelling product conveying mechanisms to move cartons and food products, would thus be stressed to extremely high limits with respect to the amount of material which may need to be processed, e.g., a conventional irradiator designed to handle 100,000 pounds per hour of grapefruit would have to handle 2,500 cartons per hour, i.e., approximately 40 cartons per minute. Conventional systems which are forced to handle cartoned products at such a rate will ultimately and undesirably damage cartons and create potential interference with the radioisotopic sources within the irradiator as the cartons move through the irradiator. Further, the mechanical design limitations imposed on systems processing such a large number of products may extend the system beyond the upper limits of appropriate mechanical design.
To accommodate such large throughputs, irradiator designs have been developed which eliminate the labor, machinery and equipment necessary to de-palletize and re-palletize products. Such irradiators are designed to automatically move entire pallets through shielding labyrinths to an irradiator source, at which time food products become irradiated on all four sides of the pallet. Upon completion of such four-sided irradiation, the pallets are automatically removed from an irradiation cell and are then placed on an outgoing truck. Such systems provide considerable savings in operating costs in comparison to the de-palletization and re-palletization systems; however, even these pallet-moving irradiator systems require relatively high labor costs for unloading and loading tractor-trailers. Once again, for throughputs of 100,000 pounds of product per hour and higher, approximately 100 pallets per hour must be processed, again putting substantial mechanical stress on any system which is designed to move such a large number of pallets. Such a system would be forced to handle two and one-half trailer loads of pallets per hour, and thus substantial material handling apparatus, e.g., loading docks, would be necessary to handle pallets at such a volume and rate. Such structure will also be unwieldy and expensive to operate.
Additionally, irradiator designs used to irradiate pallets of material require larger cell spaces than previous devices. Such larger cell spaces increase to a significant degree the amount of concrete required for the radiation shielding needed to surround such cell space. In addition, the solid angle intercepted by pallets as they are irradiated from the source is substantially reduced in comparison to the solid angle over which the cartons are conducted in carton-type irradiators. Thus, the solid angle intercepted by the pallet lowers the irradiation efficiency of utilizing radioisotopic source materials in such systems.
Accordingly, the present invention is designed to provide a transport integrated irradiation apparatus and method which overcomes many of the deficiencies of both carton-type and pallet-type conventional irradiators. The present invention will comprise a plurality of container units, i.e., irradiation canisters, which will be sufficiently large that they can receive up to approximately 10,000 pounds of produce or other foods to be irradiated. The total cost involves about one-third for irradiation, one-third for palletizing and de-palletizing, and about one-third for loading and unloading. The present system is designed to eliminate the charge for carton and/or pallet truck unloading and reloading which is inherent in the systems referred to above, as well as the charge for de-palletizing and re-palletizing cartons which is inherent in the carton system discussed above. This will leave a relatively inexpensive charge of about one-third of the overall cost of the carton system for irradiating food in accordance with the present invention.